Earlier, crashlytics required one framework - Crashlytics.framwork. Fabric requires two frameworks - Fabric.framework and Crashlytics.framework. Note that both use different Crashlytics.framework.

Reason for these errors is your project is still using old Crashlytics.framework. You just have to delete your older Crashlytics.framework and let Fabric download the newer one.

To see if your Crashlytics.framework is not updated, you can use nm which is a nifty command-line tool to see symbols in a binary.
nm Old-Crashlytics.framework will reveal same symbols present in Fabric.framework and CrashlyticsKits symbol will be missing in the list.